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Date: Fri, 10 Aug 2018 16:22:11 +0200 From: Daniel Borkmann <daniel@...earbox.net> To: Jia-Ju Bai <baijiaju1990@...il.com>, ast@...nel.org Cc: netdev@...r.kernel.org, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, brouer@...hat.com Subject: Re: [BUG] bpf: syscall: a possible sleep-in-atomic-context bug in map_update_elem() On 08/10/2018 04:07 PM, Jia-Ju Bai wrote: > The kernel may sleep with holding a rcu read lock. > > The function call paths (from bottom to top) in Linux-4.16 are: > > [FUNC] kmalloc(GFP_KERNEL) > kernel/kthread.c, 283: kmalloc in __kthread_create_on_node > kernel/kthread.c, 365: __kthread_create_on_node in kthread_create_on_node > kernel/bpf/cpumap.c, 368: kthread_create_on_node in __cpu_map_entry_alloc > kernel/bpf/cpumap.c, 490: __cpu_map_entry_alloc in cpu_map_update_elem > kernel/bpf/syscall.c, 724: [FUNC_PTR]cpu_map_update_elem in map_update_elem > kernel/bpf/syscall.c, 723: rcu_read_lock in map_update_elem > > Note that [FUNC_PTR] means a function pointer call is used. > > I do not find a good way to fix it, so I only report. > This is found by my static analysis tool (DSAC). Thanks for the report Jia-Ju! In the map_update_elem() from syscall path there's a check map->map_type == BPF_MAP_TYPE_CPUMAP, where we call the cpumap's map->ops->map_update_elem() while /not/ being under rcu_read_lock() as in other cases, so looks okay to me. Could you point out the case for being under rcu_read_lock() more specifically which the tool found? Thanks, Daniel
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